Arrangements for the unwanted coaxial withdrawal of a first cylindrical member from a second member and mechanisms for preventing this withdrawal are known. To illustrate this, spears for dispensing a liquid, e.g. beer under pressure of a drive gas, e.g. Co.sub.2 in a usually transportable container, can be considered.
In a mounted condition, the spear is fixed in a neck ring in the container by means of, for example, a screw assembly and locked in this position by means of a spring ring. The latter is placed in a groove in the neck ring, while there in the spear is a blocking face, gripping under the spring ring and thereby preventing the spear from being dismounted.
This arrangement serves a special safety purpose. If the spear is dismounted while there still is an over-pressure in the container, an accident might occur since the spear, under the subjected over-pressure, may release from the container.
However, the spring ring is not able in all cases to provide the security demanded to prevent dismounting. In some cases, the spring ring is worked into the groove by the opposite blocking face which, during the dismounting, is liable to make a movement simultaneously with the spring ring. This movement might be a rotation if the spear is mounted with a screw assembly. When the spring ring is pressed into the groove of the neck ring, it is no longer able to secure the spear from an axial displacement between the two parts.
There is, therefore, a need for a blocking arrangement of the type which is able to provide complete security against reciprocal displacement between of the two parts.